Batteries symbolize our love affair with convenience. They liberate us from wires by juicing up our smartphones, laptops and cars. With gadgets fully charged, we can go anywhere, do anything. One hundred percent power feels secure. But when the charge runs dry, we’re screwed. The good news? Engineers are trying to create the perfect battery. It is efficient and safe, and it packs a lot of oomph using little space. It’s made from abundant, cheap and nontoxic materials. It maintains a…